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Monday, April 25, 2011

As I mentioned in my previous post, I recently heard that an Europa Discovery mission has been proposed for the current mission selection. Assuming that I correctly heard the quickly made remark while listening to a meeting on the phone, it's fun to speculate what such a mission might look like. My guess is that an orbital mission with the necessary radiation hardening and the complex (and expensive) mission operations for many gravity assists to enable final entry into orbit probably is not likely.

That would leave a multiple flyby mission as the likely proposal. If a multiple Io flyby mission is compelling, then why not a multiple Europa flyby? Such a mission would not provide all the information needed to select landing sites for future missions and would not come close to replicating the depth of science a Flagship Europa orbiter would provide. During each flyby, however, such a mission could image the surface in greater resolution and coverage than the crippled Galileo orbiter was able to enhance our understanding of the processes shaping the surface. It could carry a modern infrared spectrometer to analyze surface composition in greater spatial and spectral resolution to look for locations where subsurface ocean material may have been carried to the surface. A radar sounder could measure the depth of the icy shell along the ground track below each flyby path. A magnetometer would seem a likely instrument to measure the interaction of the ocean with Jupiter's magnetosphere and continue measurements begun by Galileo.

Two types of orbits around Jupiter might be considered. The first might be a highly inclined orbit such as the one proposed for an Io multi-flyby mission that would avoid Jupiters equatorial radiation belts except for the brief time of each Europa flyby. The second would be a Galileo-style equatorial orbit that just touches Europa's orbit at each perijove. If this orbit was chosen, the spacecraft could also do multiple flybys of Ganymede and Callisto as an extended mission.

The kind of mission I've described would not replace dedicated orbiter for either Europa or Ganymede. The option to continue study of the Galilean icy moons on a Discovery budget, however, might be compelling and could mean that we don't ignore these worlds in the coming decade. The following charts from the Jupiter Europa Orbiter planning documents give an indication of the types of coverage that might be possible with a multi-flyby mission. (The JEO mission is no longer feasible given its cost and NASA budgets.) The JEO encounters with Europa were designed to pump the orbit around Jupiter down to enter orbit around Europa. As a result, the encounters occur over the same equatorial real estate. A mission designed to maximize science from flybys presumably would vary the encounter geometry with coverage more like what JEO would have done at Ganymede and Callisto.

Example of coverage from multiple flybys for four Io, six Europa, six Ganymede, and nine Callisto flybys from the planning for the Jupiter Europa Orbiter (JEO) mission. The imager on a Discovery mission might be less capable than that planned for JEO and might image smaller portions of the moons at these resolutions. All images from http://www.lpi.usra.edu/opag/feb2010/presentations/Senskev8.pdf

Example image resolutions for Europa from JEO flybys.

Example image resolution for Ganymede JEO flybys.

Editorial Thoughts: If a multi-flyby Europa Discovery mission were proposed, I worry about whether the science would be compelling enough to compete against missions proposed for other destinations. A multi-flyby mission would advance our understanding of Europa, but might not answer the fundamental questions the science community has. If not, then an eventual orbiter would still be needed. The same arguments could be made about a multi-flyby Io mission or the proposed Journey to Enceladus and Titan Discovery mission. In the case of Io, the radiation levels are so high that a follow on orbiter mission is all but inconceivable. The question, then, is when to fly a multi-flyby mission. In the case of JET, it's two instruments provide measurements that fill gaps in the Cassini mission's measurements and neither instrument requires global coverage to add significantly to our knowledge. Even so, I worry about whether review teams will consider it compelling enough for a $6-700M mission (with launch costs).

One concern for a Europa multi-flyby mission would be acquiring coverage of both hemispheres. To minimize radiation exposure, the mission likely would have its perijove, and hence maximum radiation exposure, at the orbit of Europa. (If radiation was not an issue, the perijove could be inside the orbit of Europa and have encounters on both the inbound and outbound legs of its orbit to image Titan on both hemispheres.) This makes it difficult to change the encounter geometry over a reasonable mission lifetime. Gravity assists could be used to walk the perijove around, but that would entail additional costs for a mission operations staff and a longer flight. (Editorial note: I was surprised at how expensive mission operations for the multiple gravity assists for an Enceladus orbiter would be -- it would be a substantial portion of the Principal Investigator's budget for a Discovery mission.) Perhaps mission designers have a good solution to this problem.

If I can see issues with a possible mission, then a team of experienced scientists and mission planners will have seen them, too. If an Europa Discovery mission has been proposed, it likely has clever solutions to these issues.

If ESA's Jupiter Ganymede Orbiter is selected for flight, then I hope it's mission would be enhanced to include a number of Europa flybys. One mission designer I've talked to says that the additional cost likely would be low. In this case, the mission is justified by the in-depth, global measurements at Ganymede. Flybys of Callisto and Europa would make nice bonuses.

Friday, April 22, 2011

Putting together a new Mars 2018 mission that merges two rovers -- one each from ESA and NASA -- into one while preserving the capabilities of both likely will present numerous technical problems. For ESA, it also presents political issues since ESA spending must be distributed according to national contributions to missions. Space News has a nice article on the challenges ESA faces in putting together the right plan to meet its budgeting requirements. While there is time to plan for the 2018 rover mission, this also impacts the joint 2016 Mars Trace Gas Orbiter mission for which time is short. For NASA, the two missions are separate missions with separate budgets. For ESA, this is a single program with a single budget. Indications are that ESA wants to proceed with both missions, but needs to put together a plan for approval by its member nations in May.

Thursday, April 21, 2011

The best hope for NASA missions to the icy-ocean moons of Jupiter and Saturn in the coming decade may lie in the low cost Discovery mission program. In past posts, I've described two proposals that I understand were proposed for the current Discovery mission selection competition: the Titan Mare Explorer (TiME) lake lander and the Journey to Enceladus and Titan (JET) multiple flyby mission

In addition, I understand that the Io Volcano Observer (IVO) multiple flyby mission was also proposed. As I listened to the recent Planetary Science Subcommittee meeting, I heard of a fourth proposal for a Discovery Europa mission mentioned in passing, but no details were given.

On one hand, it would seem that the prospects for Discovery missions to the outer planets are poor. The Decadal Survey considered equivalent missions to TiME, JET, and IVO, and estimated their costs at $1.4 to ~$2B, including the launch vehicle. That is well above the approximately $6-700M equivalent budget for Discovery missions. The missions studied by the Survey generally were more capable than the Discovery proposals and in the short time available for the studies were not optimized to fit within a cost target. So can more focused missions designed to cost make up the difference and allow outer planet exploration within a Discovery budget?

NASA's conditions for the current Discovery mission selection may be enabling for outer planet missions. While the principal investigator's (PI) budget for the spacecraft, instruments, operations, and analysis is similar to previous selections ($425M for this selection), NASA now pays for the intermediate class launch vehicle outside of this cost. This is an a significant boost to Discovery mission budgets. (I don't follow launch costs, and so I'm not sure of how much is this adds to the effective budget. $100-200M?) The PI for IVO has said that this change changed the budget from tight under the old rules to doable under the new rules.

In addition to the launch vehicle, for this Discovery selection, NASA will to provide a plutonium ASRG generator to power the craft at no cost to the PI. For missions beyond Jupiter, this would be an enabling technology. For missions to Jupiter, an ASRG may be enabling (solar power is an option there), but could simplify spacecraft design. For example, an Io multi-flyby mission with solar panels would require a scan platform to allow the solar panels to remain sun pointing and the instruments to point toward Io. With an ASRG, the craft can skip this expense and use the entire spacecraft to point the instruments as the Cassini spacecraft does. NASA previously has said that it intends to make ASRGs an option for every other Discovery selection, although I've not heard what they expect to do under the new post Decadal Survey plan to select Discovery missions more frequently (every two years instead of every 3-4 years).

Proposals for outer planet Discovery missions face two hurdles. First, they must be credible and convince the review teams making the selection that they are technically and financially feasible within the Discovery budget. Second, they must be compelling and offer better science than proposals to other destinations. Here, the narrow focus and the long flight times (with operations costs of $7-10M per year, I've heard) may hurt. JET, for example, carries two instruments that would significantly advance our knowledge of Titan and Enceladus. Would a mission to, say, Venus or a comet with five or six instruments provide more compelling science for the dollar?

In the next few weeks, we should learn which three of the 28 proposals (including the outer planet proposals) will become finalists in the current selection for further study to eventually select the winning proposal. If an outer planets mission is among the selections, that would suggest that outer planet Discovery missions are possible. Unless an outer planets mission is eventually selected for flight, however, we won't have a conclusive answer to whether outer planet Discovery missions can clear these two hurdles. The team that has proposed the OSIRIS-REX asteroid sample return New Frontiers mission, originally proposed a similar Discovery mission that was a finalist in a previous selection. The team has reported that while they received top science scores (i.e., the mission was compelling) in the final analysis the mission was judged to be too expensive for the then Discovery mission budget limit.

Editorial Thoughts: I am encouraged by the teams that have proposed outer planet Discovery missions. They include a long list of credible, experienced researchers in planetary exploration who have been around the block a few times. If they are willing to put the time and energy into these proposals, then I feel there's reason for optimism balanced with the observation that outer planet missions inherently carry more costs than equivalent missions to the inner planets. We may know more soon when the current finalists are announced.

Tuesday, April 19, 2011

As NASA has time to reflect on the implications of the now six week old Decadal Survey and its new budget projections, more details on planning for the coming decade are emerging. The head of the Planetary Science Division gave the latest account of current plans at a meeting of NASA Advisory Council’s Planetary Science Subcommittee on April 18.

The laid out plans for Discovery and New Frontiers missions over the coming decade. The announcement of opportunity (AO) that begins the selection process for the next Discovery mission should be in sometime in 2013 (~36 months after the previous AO). After that, AO's should be issued every 24 months. That will mean the selection of 4-5 new Discovery missions over the coming decade, including the the selection in progress. New Frontiers AOs will continue to be issued every five years, with the next AO due around 2015.

Much of the presentation repeated information that I've presented in previous posts on the ramifications of the Decadal Survey's recommendations and NASA's budget. A few tidbits from the presentation are:

From the presentation, it appears that the selection of three finalists for next Discovery mission will be in April/May. Selection of the next New Frontiers mission apparently will be in May/June.

Planning of a new joint ESA/NASA Mars 2018 rover and sample cache mission is underway. A key decision by ESA on whether to proceed or not will occur at a meeting on May 26/27. Space News has an article on the early thinking behind a redesigned mission. From the article, it appears that NASA would contribute $1.2B to the joint mission. With ESA's contribution, this would be a mission on the financial scale of the Mars Science Laboratory planned for launch this year.

Restart of plutonium-238 production was not authorized in the continuing resolution funding NASA for the rest of FY11.

Technical studies for a smaller Europa mission will be done over the next two years. Such a mission presumably would fly only if the budget picture improves sufficiently to add a Flagship mission to the budget.

Wednesday, April 13, 2011

At long last, there is agreement on a budget for NASA for FY11 (just six months into the fiscal year). For NASA's science program, the final agreement can be viewed as either an increase over FY10 ($4945M compared to last year's $4469M for an increase of $476M) or a small cut compared to the President's original FY11 budget proposal ($60M less). I have not seen details on how the budget will be distributed within the Science program, but the Planetary program likely to make out relatively well.

Monday, April 11, 2011

Several weeks before the release of the Decadal Survey’s report, a special meeting of the Outer Planet Analysis Group (OPAG) was scheduled for the week following the release.It was the only one of the analysis groups (there are also ones for Venus, the moon, Mars, and small bodies) to schedule a special meeting.It was a strong hint that the report was not going to have good news for the outer planets community.

For several years, the exploration of the icy-ocean moons Ganymede, Europa, Titan, and Enceladus has been the highest priority of the outer planet research community. The Survey attempted to enable a vibrant outer planets program with three flagship missions on the recommended list (Europa and Enceladus orbiters and a Uranus orbiter and probe mission) and Io and Saturn probe missions on the New Frontiers candidate list.In plusher budget times, the outer planet program would have been a big winner.

In the new leaner budget times, if there was a category of missions that was loser in the collision between he Decadal Survey’s recommendations, and the new budget realities for NASA’s planetary program, it was the icy-ocean moon missions.The flagship missions now appear unaffordable.The Io and Saturn probe missions do not address the icy-ocean moons.

Now, further exploration of these moons rests on the European Space Agency’s (ESA’s) possible Ganymede orbiter that is in competition with two good astronomy/astrophysics missions for selection.

The OPAG report from the meeting following the Survey report may be a first step in asking NASA to look for new approaches to enabling the exploration of icy-ocean moons.The official report strongly endorses the Decadal Survey recommendations.(You can read the report at http://www.lpi.usra.edu/opag/mar2011/meetingReport.pdf).The closest OPAG came to suggesting a re-examination was a request to pursue non-Flagship outer planet missions and to consider technology improvements that might enable Titan missions.

I listened to a good portion of the meeting, and there were several requests to see if it would be possible to add an icy-ocean mission to the list of New Frontiers candidate missions mid decade.(Unlike the Discovery missions that can be proposed for any target, New Frontiers missions are selected from a candidate list.Proposals for the ~$650M-$1B New Frontiers missions are so expensive to prepare that the list is kept short so that proposing teams can focus their resources.)There is precedence for such a request to change the New Frontiers list.The previous 2003 Decadal Survey recommended four candidate missions, and the list subsequently was expanded mid decade.In addition, the new Survey report states that possible New Frontiers class missions to the icy-ocean moons were not prioritized (and Ganymede was dropped from the previous list) at least in part because of the priority given to a now unlikely Europa flagship mission.

Any decision to re-examine the New Frontiers candidate list properly belongs several years in the future.In my next post, however, I’ll start looking at tactics and missions that might enable continued exploration of these moons in the coming decade.

Friday, April 8, 2011

The latest news reports that an agreement was reached at the last moment and there will be no government shutdown.

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With less than five hours to reach an agreement between deadlocked political parties, it looks increasingly likely that at least a short U.S. federal government shutdown will occur. Space News has an article on NASA's shutdown plans that contains some good news. While mission development generally will be suspended, contractors using previously obligated funds can continue their work. Both planetary missions with critical launch windows, the Mars Science Laboratory and the Juno Jupiter orbiter, are being developed by JPL, a NASA contractor. In the case of Juno, the spacecraft is being built by Lockheed Martin Space Systems, by a private contractor. JPL and Lockheed Martin also are managing the development of the GRAIL lunar obiters. Therefore, according to the article, work on these missions can proceed at least until NASA employees or NASA facilities would have to become involved. The article does not address how launch preparation work would be effected, although I believe the actual launch services are provided by contractors.

In addition, mission operations will continue for all missions currently in flight.

Thursday, April 7, 2011

Several good articles out with interesting news on future planetary missions.

The first story potentially portends bad news for NASA's planetary program. For readers living outside the U.S., the federal government has no authority to spend money if Congress has not passed and the President has not signed a budget for the current year. We're more than halfway through FY11 without a budget, and the government has been operating on continuing resolutions with the current one set to expire tomorrow (Friday April 7). The two political parties are at logger heads and it looks like the government may shut down as of Saturday. Critical functions will continue to operate, including operation of all missions currently in flight. According to NASA Watch, however, missions in development will cease development.

Editorial Thoughts: NASA has three missions -- the Mars Science Laboratory, the Juno Jupiter orbiter, and the GRAIL lunar mission -- in the late stages of preparation for launch this year. If a shut down occurs and lasts long enough, NASA might not be able to complete preparations for launch this year. The next opportunity to launch to Mars would come in approximately 26 months and to Jupiter in approximately 13 months. Having to store these spacecraft and keep the mission teams together would be expensive.

Editorial Thoughts: The original mission plan had the ESA rover focused on sophisticated chemical analyses of samples drilled from up to two meters below the surface. The NASA rover's primary task was to collect and cache samples, but it would have sophisticated instruments on its arm to investigate rocks and soil on the surface. A rover that combines these capabilities would, in my opinion, be a kick ass mission. The Mars Science Laboratory will explore the chemistry of Mars in-depth at one site; the 2018 mission would add a second site and subsurface sampling.

Saturday, April 2, 2011

The Decadal Survey studied a large number missions in depth and recommended only a handful as candidates for flight this coming decade. Why were the rest not prioritized? Going through the entire list can make for tedious reading (trust me, I did it). However, there are some highlights that represented interesting trends.

All quotes are from the Survey report.

Dropped to Maintain Balance

As I noted in the previous post (which was originally intended as just a sentence in this post), a key goal of the recommended program is maintain a balanced program. If a target or class of targets already had a Flagship mission recommended, then other good missions to the same or similar targets were not prioritized. Some examples:

Ganymede Orbiter—"This mission's primary science objectives are the characterization of the satellite's subsurface ocean, geology, magnetic field, and origin... Consideration of the Ganymede Orbiter is deferred to the decade following 2013-2022 because of its lower science return per dollar relative to the JEO [Jupiter Europa Orbiter] mission, and because EJSM [Europa Jupiter System Mission] as currently envisioned would include an ESA-provided spacecraft to study Ganymede, making this mission largely redundant."

Mars Geophysical Network—"The primary science objectives of this mission are to characterize the internal structure, thermal state, and meteorology of Mars... Consideration of the Mars Geophysical Network is deferred to the decade following 2013-2022 because of its lower scientific priority relative to the initiation of the Mars sample return campaign. "

Enceladus orbiter - "...because of the broad similarity of its science goals to those of JEO, NASA should consider flying the Enceladus Orbiter in the decade 2013-2022 only if JEO is not carried out in that decade."

Not Enough Bang for the Buck

Neptune/Triton/KBO Mission - "The flyby mission architectures were deemed to achieve significant science progress since Voyager 2's visit of Neptune and offer the potential for new KBO science. Even the simplest of the flyby missions exceeded the cost cap of a New Frontiers mission and offered low science return relative to its cost, it was deemed not compelling. More complex missions and orbiters provided a vast gain in science objectives unavailable to flyby missions, but at increased cost; the highest performance option yielded a modest increase in estimated science value for its higher cost. More detailed design work of a “sweet spot” mission design identified technical risks that make a Uranus mission more favorable for the coming decade. Technology development will increase the feasibility of a future Neptune orbiter mission."

Titan Lake Probe- "The exploration of Titan's hydrocarbon lakes has high scientific potential and the Titan lake lander concepts appear feasible. However, based on the costs and the relatively limited science scope of a stand-alone lake probe without the orbiter and balloon elements, the stand-alone lake probe concepts were judged to be lower priority than a lake probe which was an element of a flagship mission, or some of the other mission concepts studied."

Venus Tessera Lander - "The most significant challenges posed by this mission were related to the development of a high- TRL [technical readiness level for flight] level Raman/laser-induced breakdown spectroscopy (LIBS) system, safe landing, and testing at Venus environmental conditions. To reduce risk, advancements in two key technology areas are needed: first, verifying the Raman/LIBS implementation, calibrated operation, and sizing for the Venus surface environment, including high entry loads on the laser and second, additional analyses and testing to ensure safe landing in potentially rugged terrains (at lander scales)."

Mercury lander - "Because of the complex and challenging nature of this mission, a more detailed characterization study is recommended before moving forward with the Mercury Lander concept. Both SEP [solar electric propulsion] and ballistic trajectory approaches and concepts should be further explored with a more detailed mission design and concept definition to determine the preferred mission implementation approach. Currently each has benefits and risks that could not be fully characterized at this level of study."

Chiron orbiter - "Of the five propulsion options considered for trajectories into Chiron orbit, the all-chemical option did not deliver a viable payload. The two solar-electric and chemical propulsion options delivered useful masses with reduced science payloads. Finally, the two radioisotope-electric propulsion (REP) options delivered a viable payload capable of meeting all science requirements. However, the REP system will likely need more than the two ASRGs assumed available for this mission. This study demonstrated the need for continued investments in long-term communication infrastructure and propulsion technologies before such missions could be attempted."

Just Didn't Make the Cut

Lunar Polar Volatiles Explorer - "A lunar polar volatiles mission represents an important opportunity to study the nature, composition and dynamics of volatiles trapped in the frigid interiors of lunar polar impact craters. It also provides an opportunity to investigate polar volatiles, especially water ice, as a potential resource for future human exploration of the Moon and destinations beyond. Although such a mission retains a high science value, the polar crater environment presents a number of technical challenges, including rover survivability, sample collection and characterization, and navigation. Although some technical maturation is required, there remain no major impediments to such a mission within this decade. "

Editorial Thoughts

The loss of outer planet Flagship missions in the coming decade with new budget forecasts makes the choice to not prioritize the Ganymede Orbiter or an Enceladus mission unfortunate. The icy-ocean moons have been the top priority for outer planet exploration, and now there are no viable missions in the candidate list for the coming decade. If the Decadal Survey committees had known this ahead of time, they might have commissioned mission studies for highly focused flights to these worlds that might fit within the New Frontiers program. For example, the recommended candidate Comet Sample Return mission has a cost estimate of $1.6B, which is near the cost for the Enceladus Orbiter at $1.9B. There may have been ways to reduce missions costs for an Enceladus mission to come in within the range of the New Frontiers cost cap.

Note the technical issues mentioned for the Titan Lake Probe and the Venus Tessera Landers. Similar missions are currently proposed for the Discovery and New Frontiers programs, respectively. The proposers hopefully have good solutions to these issues; if not, this may not bode well for these proposals.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.